The present invention relates generally to medical device deployment systems and more particularly to trigger wires used in low-profile delivery systems for self-expanding medical devices.
The use of trigger wires in delivery systems to retain and release self-expanding medical devices is well-known in the art. As used in the present application, “proximal” and “distal” are defined relative to the heart. Trigger wires typically retain a self-expanding medical device by forming a bend around a portion of the self-expanding medical device, and release the self-expanding medical device when the trigger wire is withdrawn proximally through the delivery system so that the trigger wire no longer forms a bend about the medical device. Known trigger wires are of constant cross-section. Thus, trigger wires must restrain the self-expanding medical device during delivery, be capable of being withdrawn through the delivery system, and provide an adequate connection to a handle at the distal end of the trigger wire.
Different levels of bending and tensile strength are required for each of the functions a trigger wire must perform. For example, a certain level of bending strength is required at the proximal portion of the trigger wire where the trigger wire retains the medical device, and a certain level of bending strength is also required at the distal portion of the trigger wire where the trigger wire connects to the handle. The center portion of the trigger wire only requires adequate tensile strength as an operator withdraws the trigger wire through the delivery system.
Delivery devices for self-expanding medical devices are typically advanced through a body vessel to a treatment site. Thus, it is advantageous to minimize the size of delivery devices to allow operators to place self-expanding medical devices in smaller body vessels, and to minimize potential trauma to body vessels as the delivery device passes through. A lower-profile device is also advantageous because it is easier to navigate through tortuous vasculature. Additionally, a lower-profile delivery device is advantageous to allow an operator to position or use other medical devices in the body vessel simultaneously with the delivery device.